For the second test in our astronomy class.
Key Concepts
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How did the motions of the planets shape the history of astronomy?
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What were the major contributions of Ptolemy, Copernicus, Brahe, Kepler, and Galileo? What are Kepler’s Laws?
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How do we describe motion? What are Newton’s Laws and why are they so important?
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What is the Universal Law of Gravitation? How does it relate to tides?
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What is energy? What is meant by a conservation law, and specifically, the conservation of energy. What are some of the different forms of energy?
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What are the main objects in our solar system?
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What are some of the interesting properties of our solar system? How did our solar system form?
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How old is the solar system? How do we know?
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What is the structure of the terrestrial planets? What types of atmospheres do they have? How do the properties of the planets relate to one another? What geological processes shape the surfaces of the terrestrial worlds?
Summary
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Planetary Motions and Astronomy History: Observing planets’ motions led to key astronomical insights and models. Early astronomers noticed the irregular paths of planets, which challenged Earth-centered views and inspired models that eventually confirmed a heliocentric (sun-centered) system.
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Contributions of Key Astronomers:
- Ptolemy: Created the geocentric model with epicycles to explain planetary motion.
- Copernicus: Proposed the heliocentric model, placing the Sun at the center.
- Brahe: Provided precise planetary data that enabled further discoveries.
- Kepler: Used Brahe’s data to establish his three laws of planetary motion.
- Galileo: Observed moons of Jupiter, phases of Venus, supporting heliocentrism.
- Kepler’s Laws: 1) Planets move in elliptical orbits. 2) They sweep equal areas in equal times. 3) The square of a planet’s orbital period is proportional to the cube of its semi-major axis.
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Describing Motion and Newton’s Laws: Motion is described by position, velocity, and acceleration. Newton’s Laws—1) Inertia, 2) F=ma, and 3) Action-reaction—explain motion’s causes and predict planetary behavior, laying the foundation for classical mechanics.
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Universal Law of Gravitation and Tides: Newton’s Universal Law of Gravitation states that any two masses attract with a force proportional to their masses and inversely proportional to the square of their distance. This explains tides, as the Moon’s gravity pulls differently on Earth’s near and far sides, creating tidal bulges.
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Energy and Conservation Laws: Energy, the ability to do work, exists in various forms (kinetic, potential, thermal, etc.). The conservation of energy states that energy in a closed system remains constant, crucial for understanding physical processes in the universe.
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Main Solar System Objects: The solar system includes the Sun, eight planets, dwarf planets, moons, asteroids, comets, and the Kuiper Belt objects.
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Solar System Properties and Formation: Our solar system’s nearly circular, coplanar orbits, and the distinction between rocky inner and gas-giant outer planets suggest it formed from a rotating disk of gas and dust about 4.6 billion years ago.
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Age of the Solar System: The solar system is approximately 4.6 billion years old, determined by radiometric dating of Earth’s oldest rocks and meteorites.
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Structure and Atmospheres of Terrestrial Planets: Terrestrial planets (Mercury, Venus, Earth, Mars) have rocky crusts, mantles, and metallic cores. Their atmospheres vary: Earth has a balanced, life-supporting atmosphere, while Venus and Mars have thick and thin CO₂-rich atmospheres, respectively. Geological activity, such as volcanism and tectonics, shapes their surfaces.
Terms
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displacement
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velocity
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speed
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acceleration
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force
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momentum
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Newton’s Laws
In the first law, an object will not change its motion unless a force acts on it. In the second law, the force on an object is equal to its mass times its acceleration. In the third law, when two objects interact, they apply forces to each other of equal magnitude and opposite direction
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ellipse
In astronomy, an “ellipse” refers to the oval-shaped path that planets and other celestial bodies follow around the Sun, meaning their orbits are not perfect circles but instead take on an elliptical shape, with the Sun situated at one of the focal points of the ellipse; this is a fundamental concept described by Kepler’s First Law of Planetary Motion.
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focus
Focus is a point where rays of light or other radiation converge or from which they appear to diverge. In astronomy, it often refers to the points in an elliptical orbit around which celestial bodies revolve.
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semimajor axis
one half of the major axis and equal to the distance from the center of the ellipse to one end of the ellipse. It is also the average distance of a planet from the Sun at one focus.
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Kepler’s Laws
(1) planets move in elliptical orbits with the Sun as a focus, (2) a planet covers the same area of space in the same amount of time no matter where it is in its orbit, and (3) a planet’s orbital period is proportional to the size of its orbit (its semi-major axis).
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Eccentricity
the extent to which an orbit is elliptical or deviates from a perfect circle. A perfectly circular orbit would have an orbital eccentricity of 0. Values between 0 and 1 indicate an elliptical orbit, increasing numbers have a greater distance between the foci in the ellipse.
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Weight
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Universal Law of Gravitation
Newton’s law of universal gravitation states that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
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inverse square law
the intensity of a physical quantity decreases as the distance from its source increases, and that this decrease is proportional to the square of the distance
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tidal force
the gravitational effect that causes tides and other phenomena. It’s caused by the difference in the strength of gravity between two points, such as the Earth and the Moon.
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spring tide
a phenomenon that occurs twice a month when the gravitational forces of the sun and moon combine to produce higher high tides and lower low tides
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neap tide
a moderate tide that occurs when the sun and moon are at right angles to each other, partially canceling out each other’s gravitational pull on the ocean
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tidal friction
the result of a celestial body’s cyclic gravitational variations causing strain on the body, which dissipates tidal energy
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synchronous rotation
when an object rotates on its axis at the same rate as it orbits another body, causing the same side of the object to always face the other body
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momentum
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kinetic energy
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potential energy
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radiative energy
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temperature
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Kelvin scale
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terrestrial planet
a planet that is made up of rocks or metals and has a solid or liquid surface
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jovian planet
a gas giant, or one of the four outer planets in our solar system
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asteroid
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comet
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solar nebula
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condensation
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accretion
a fundamental process in astronomy that describes how gravity causes matter to accumulate and form larger objects
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planetesimal
celestial bodies that are the building blocks of planets and are a key part of planetesimal astronomy
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nebular theory of solar system formation
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frost line
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protoplanetary disk
a rotating disk of gas and dust that surrounds a young star
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condensation
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accretion
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radiometric dating
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half-life
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core
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mantle
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crust
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lithosphere
the rigid, rocky outer shell of a terrestrial planet or natural satellite
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differentiation
the process by which a planetary body’s materials separate into distinct layers based on their densities and chemical properties
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heat transfer
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conduction
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convection
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radiation
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volcanism
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tectonics
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erosion
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atmosphere
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pressure
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greenhouse effect
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maria
large, dark, flat plains on the Moon that are the result of lava flows filling impact basins